FPS and Joule Converter

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FPS and Joule Converter

Post by Dominum » Wed Sep 30, 2009 7:33 pm

http://asgcalc.hollved.com/us/index.php

^This link can convert Joules and FPS with various weights of BBs. 400 FPS with a .20 is NOT the same as 400 FPS with a .25, etc.
Last edited by Dominum on Fri Mar 12, 2010 8:18 pm, edited 1 time in total.
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Re: FPS and Joule Converter

Post by Vesper » Mon Oct 05, 2009 7:23 pm

Good stuff, Dom.

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Re: FPS and Joule Converter

Post by 6mmSilver » Tue Oct 06, 2009 4:28 pm

So, let me get this straight, shooting at 450 fps with .2 gram hurts just as much if you a higher gram BB?
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Re: FPS and Joule Converter

Post by Tzer1993 » Tue Oct 06, 2009 4:30 pm

Yes...I've thought about it and maybe a heavier bb would keep more momentum so at a close distance it may hurt a bit more but it doesn't really matter

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Re: FPS and Joule Converter

Post by Dominum » Tue Oct 06, 2009 4:34 pm

Energy transferred to a target (Joules) is the combination of both it's speed AND it's weight. A .25g projectile is heavier than a .20g projectile, and thus if they are fired at the same speed the heavier one will impart more energy.
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Re: FPS and Joule Converter

Post by Dominum » Tue Oct 06, 2009 4:37 pm

6mmSilver wrote:So, let me get this straight, shooting at 450 fps with .2 gram hurts just as much if you a higher gram BB?

If your gun shoots a .20 at 450 FPS, it will fire a .25 at 402 FPS. Both projectiles will impart the same Joules (energy transferred). A .25 fired at 450 FPS is NOT equivalent to a .20 fired at 450 FPS.
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Re: FPS and Joule Converter

Post by 6mmSilver » Tue Oct 06, 2009 4:38 pm

Gotcha, Thanks Guys.  ;)
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Re: FPS and Joule Converter

Post by Pyrus_Conflagarus » Wed Nov 24, 2010 9:25 pm

Why use a fancy program when the math is so easy.
Kinetic Energy  (KE) =1/2 Mass * Velocity^2

Note: ft/sec is an English Engineering System unit of speed, and a Joule is a metric unit of energy. Therefore you will have to convert your muzzle velocity to m/sec. Also, the fundamental units of the Joule are (kg*m^2)/sec^2, therefore you will have to divide the end result by 1000g to get Joules

As for the question about the mass to KE ratio of a bb (contrary to popular belief, BBs are classified by their MASS, not their WEIGHT. Big, big difference between the two) consider this:
at 400 ft/sec, a
.20g bb has 1.486J of KE
.25g bb has 1.858J of KE
.28g bb has 2.081J of KE

Now looking at that last figure, consider this. My M700 pumps out bbs at ~2.810J. That translates to 550 ft/sec w/.2g bbs.

Fancy programs are convenient and all, but knowing how everything works is way more awesome.
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Re: FPS and Joule Converter

Post by D.Smitty » Wed Nov 24, 2010 10:17 pm

As an analogue to this information, it should be known that bbs, once fired from their guns, do NOT slow down at the same rates.  This makes sense, as anybody should realize that a heavier bb (at any elevation we will be shooting at, using weight or mass units will not make a difference) will be able to cut through the air better than their lightweight cousins.

Reference Navier-Stokes equations (specifically, Stokes' Law) for the details if you wish (you probably don't), but the quick and dirty of it is that the mass of the bb does not affect the amount of force the air exerts on the bb.  This means that, while they have a lower velocity out of the gun, heavier weight (or mass if you want to be all meh about it) bbs have will have more kinetic energy left when they reach a target at the same range. 

It's not just a coincidence that snipers with those 0.43s can make you stop and reconsider stepping in their line of fire!  It's science!
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Re: FPS and Joule Converter

Post by Pyrus_Conflagarus » Thu Nov 25, 2010 10:52 am

D.Smitty wrote:As an analogue to this information, it should be known that bbs, once fired from their guns, do NOT slow down at the same rates.  This makes sense, as anybody should realize that a heavier bb (at any elevation we will be shooting at, using weight or mass units will not make a difference) will be able to cut through the air better than their lightweight cousins.

Reference Navier-Stokes equations (specifically, Stokes' Law) for the details if you wish (you probably don't), but the quick and dirty of it is that the mass of the bb does not affect the amount of force the air exerts on the bb.  This means that, while they have a lower velocity out of the gun, heavier weight (or mass if you want to be all meh about it) bbs have will have more kinetic energy left when they reach a target at the same range. 

It's not just a coincidence that snipers with those 0.43s can make you stop and reconsider stepping in their line of fire!  It's science!


ooh, that reminds me. I now have an opportunity to test something I was having a debate about back in Colorado: the effects of altitude on gun performance.  Basically the question was whether the hicher air denity at sea level would have any effect on performance as compared to what you would get in the mountains of Colorado.






I need to go chrono something now... ;)
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Re: FPS and Joule Converter

Post by Doublewolf » Thu Nov 25, 2010 12:35 pm

Can't most chronographs measure joules? If you can test it and see if it can accurately detect the difference in energy between different weights of BBs, it would be helpful. These are examples of how it might help:

1. Although not usually an issue, prevent cheating
2. You could chrono with any weight of bbs you wanted (last game I had to borrow some because I had no .2s.)
3. Just make things easier.

I suggest testing this method. It might not work; I am unsure if the chrono could accurately measure energy, not just speed. If it does work, though, It could be beneficial.

If not, maybe a conversion chart so that you could use different weights of bbs. It would be easy to make with that program. I'll even do it, if you want.

Also, this has been explained above, but I'll say it anyway. Because of the law of inertia, objects with larger masses require more force to stop. Higher weight bbs will resist a change in motion more than lower weight bbs, and they will stay going fast for a longer time, and hit you harder.
Last edited by Doublewolf on Thu Nov 25, 2010 12:41 pm, edited 1 time in total.


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Re: FPS and Joule Converter

Post by SteevoLS » Thu Nov 25, 2010 1:21 pm

I can't speak for every chronograph, but most simply detect motion. That joule rating is based on an arbitrary set of characteristics.
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Re: FPS and Joule Converter

Post by Veimos » Fri Nov 26, 2010 1:25 am

Doublewolf wrote:Can't most chronographs measure joules? If you can test it and see if it can accurately detect the difference in energy between different weights of BBs, it would be helpful. These are examples of how it might help:

1. Although not usually an issue, prevent cheating
2. You could chrono with any weight of bbs you wanted (last game I had to borrow some because I had no .2s.)
3. Just make things easier.

I suggest testing this method. It might not work; I am unsure if the chrono could accurately measure energy, not just speed. If it does work, though, It could be beneficial.

If not, maybe a conversion chart so that you could use different weights of bbs. It would be easy to make with that program. I'll even do it, if you want.

Also, this has been explained above, but I'll say it anyway. Because of the law of inertia, objects with larger masses require more force to stop. Higher weight bbs will resist a change in motion more than lower weight bbs, and they will stay going fast for a longer time, and hit you harder.


Joules ,for what we reference them for in airsoft, are detected at impact.  For chrono's that "detect" joule's, you have to input the weight of the bb.  At that point it takes the FPS and does the math.  So unless you are  weighing the bb, you are still taking the persons word for it.  You would need some kind of impact pad setup to measure joules.  For a general rule of thumb, (and correct me if I'm wrong), for every .10 gram of weight you are above .20, you add 100 fps.  So if the fps limit is 400 for full auto, and you're using .30 bb's, AND are shooting at 350 fps, you would be shooting at 450 fps if it were a .20.  So you would be 50 fps over the 400 limit and would have to shoot said weapon in semi only.
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Re: FPS and Joule Converter

Post by D.Smitty » Fri Nov 26, 2010 1:46 am

Pyrus_Conflagarus wrote:ooh, that reminds me. I now have an opportunity to test something I was having a debate about back in Colorado: the effects of altitude on gun performance.  Basically the question was whether the hicher air denity at sea level would have any effect on performance as compared to what you would get in the mountains of Colorado.


I would assume that by "performance" you are referring to the fact that AEGs and spring guns use a cylinder which compresses air through a nozzle to fire a bb.  You are right to say that being at a higher altitude would mean that air is less dense, and therefore, the same volume of space would not hold the same volume of air.  This means that your cylinder would be pushing less air to propel your bb.  Gas guns shouldn't be affected by this effect (thought the lower temperature would affect them).

There are three things about that I should point out. 
First, nobody's cylinder uses all the air to propel their bb; it takes time for the cylinder to compress all that air out of that small nozzle.  As soon as a little air starts to hit the bb, the bb starts moving, then you start to lose air pressure around the sides and past the bb (even with a .01 barrel).  This will tend to reduce any changes if FPS that might come from changes in the air composition and density.
Secondly, the fact that there is less air means that your spring has an easier time pushing on your piston, meaning that it will push the piston faster (will not increase your ROF, though, that's that motor and gears).  This will tend to mitigate the effect.
Thirdly, while the density of air DOES change with elevation, the fact that you can still breath that air can tell you that the pressure and density are not all that different (human body is not very tolerant of pressure variations).  This suggests that any changes will be insignificant.

While I have not proven anything, I would say that any changes that come from firing guns in different places are best learned by firing guns in different places.  Let your weapon do the science and remember what changes you need to make.
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Re: FPS and Joule Converter

Post by D.Smitty » Fri Nov 26, 2010 1:50 am

Doublewolf wrote:Can't most chronographs measure joules?


When manufacturers started advertising that chornographs would measure joules, folks got excited for this very reason.  Sadly, a chronograph is simply a chronograph (measures speed of bb, nothing more, nothing less).  The display of joules simply makes the calculation before the display based on a 0.20 g bb (that being the standard weight).  Something that measures the kinetic energy of the bb directly would have to be something the bb hits directly and imparts its kinetic energy into.  Not an efficient direct measurement.
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